Funny... I was at a Climb for Life event in September and Michael Reardon asked me the same thing. I was speechless, and he said, "me too." The easier concrete reasons are the social aspects... climbers are generally very interesting people. I love being with the rocks and the bugs and leafy greenlies too. Of course I have some more profound reasons (like that climbing actually saved my life in some ways), but, for here and now, I'll leave it at that.